Hexagonal Printed Monopole Antenna with Triple Stop Bands for UWB Applications

Inherently UWB (Ultra Wideband) communication systems comes with interference problem with some of the existing narrowband communication systems. These bands are stopped with the help of band-stop filter in order to reduce electromagnetic interference. However, the complexity and limitations are increased due to these filters, hence this solution is turned down in those applications where design complications and complexity is of concern. Introducing various slots of specific shapes and exact dimensions however, have solved this issue for the researchers around the world. This paper presents a hexagonal PMA (Printed Monopole Antenna) with triple stop bands. The antenna is used for UWB application. The antenna is stopped the WiMAX (Worldwide Interoperability for Microwave Access), WLAN (Wireless Local Area Network) and ITU (International Telecommunication Union) bands. The antenna dimensions are 30x28x16 mm 3 . FR4 is used between ground and radiating patch with relative permittivity of 4.4. The VSWR (Voltage Standing Wave Ratio) is less than 2 between 3-11 GHz except WiMAX (3.1-3.7 GHz), WLAN (5.1-5.8 GHz) and the ITU frequency band (7.95-8.4 GHz). The antenna is design in CST software.


INTRODUCTION
WiMAX and ITU. These bands are stopped with the help of band-stop filter in order to reduce electromagnetic interference. However, the complexity and limitations are increased due to these filters. Therefore, the PMA with notched characteristics is required to reduce the interference, which is very simple, low profile, compact in size, easy in installation and fabrication.
The stop band antenna with size of 30x30x1.6 mm 3 is propounded, the dual band are stopped with the help of slots in radiator and ground [3]. The PMA with stop band characteristic is presented, the size of the antenna is 48.7x42mm [4]. Liu et. al. [5] designed notched band antenna with large size of 40x40mm. The dual stop band circular design with size of 35.5x30x1.6mm is propounded, the antenna is printed on FR4 substrate [6]. The U shaped antenna with dual notched band is proposed, the bands is stopped with CSRR (Complementary Split Ring Resonator) and T shaped slot and the size of antenna is 24.6x38.1 mm 2 [7]. The triple notched band antenna with dimension of 24x34.6 mm is designed, the height of substrate is .8mm [8]. The circular antenna is presented to stop triple bands by using square short resonator, the size of the antenna is 40x20x0.508 mm 3 [9]. The PMA with size of 60x60x1.6 mm 3 is designed, the author used various shaped slot and F shaped stub to stop various bands [10]. The PMA is proposed with the rejection of two bands with the help of two slots, the dimension of the design is 31x31x1.15 mm 3 [11]. The single stop band PMA with circular slot is propounded, the size of the antenna is 50x50x0.5 mm 3 [12].
Recently various stop band printed antennas are reported where the band are stopped due to SRR, CSRR, open loop resonator, parasitic strips and embedded T shaped stub [13][14][15][16]. The interference of existing narrow bands are also reduce due to introducing different shapes of slot in radiator patch, ground and feed line such as Tshaped, E-shaped slot, symmetrical elliptical slots, fractal shaped slot, C-shaped slots, inverted C-shaped slots, semi-elliptical slot, U-shaped slot, L-shaped slot, circular slot and rectangular slot [17][18][19][20][21][22][23][24]. The detailed comparison is given in the Table 1.
In this paper, simple hexagonal PMA is presented which  The height of the ground is 8mm and width is 28mm and various other parameter is discussed in Table 2. The antenna is fed with 50&! transmission line. The complete antenna design is depicted in Fig. 1(a-b) and its S 11 is shown in Fig. 2. The VSWR of proposed antenna is also illustration in Fig. 3. The length of slots can be calculated from bellow postulate [3].   (2) L s1 denotes the length of rectangular slot, L s2 denotes the length of U shaped slot, f n is notch frequency and  r is relative permittivity. The rectangular slot is /4 at stop band frequencies and remain two slots are /2 at stop band frequencies.

RESULTS AND DISUCUSION
The VSWR is less than 2 between 3-11GHz except  Fig. 5(a-c). In E-plane the pattern is same to dipole antenna and in H-plane the pattern is nearly omni-directional.   The vector current distribution at different notched frequencies are given in Fig. 6(a-c). The current is flowing around rectangular slot but in opposite Gain (dB) Similarly, the 5.5 and 8.1GHz band are stop due to U shaped and inverted U shaped slot which is clearly illustrated in Fig. 6.
The photographical image of presented design is depicted in Fig. 7(a-b). The design is tested through Agilent Technologies Network Analyzer N5242A. The measured and simulated S 11 and VSWR is shown in Figs. 8-9 respectively. The slight shift occurred due to SMA connecter and Fabrication error.
the complexity and limitations are increased due to these filters. The aim of the research is to design compact size PMA with band stop characteristics to reduce interference with existing narrow bands. Therefore, the PMA with notched characteristics is required to reduce the interference, which is very simple, low profile, compact in size, easy in installation and fabrication. The antenna is resonating from 3-11 GHz except stop bands. The slots are introduced to stop the bands of WiMAX, WLAN and the ITU frequency band.